Forum Replies Created
-
Posts
-
The difficulty you may find is converting the output from HOPS into one of the file formats used by the BAA. If that is difficult, then don’t bother.
Hi Andy,
Yes, quite tricky! It’s the comparison stars that are hard to deal with. As far as I can see, exploring the various output files, the pixel co-ords of the comp stars are stored in the log.yaml file, but no details about them. I could locate them on a chart and then enter that data but it will certainly be fiddly!
Cheers
Ian.How I would deal with this is to write a few scripts. It’s what I did a few years ago to upload to the BAA database.
First make sure that at least one of the images showing the target and the comparisons has an accurate WCS. If none do, astrometry.net, either on-line or self-hosted (my solution).
The coordinates of the target star are presumably well known, what are not are those for the comparisons but if you have a list of (x,y) coordinates and a WCS, the xy2sky program from the WCS tools utilities will produce a list of (RA,Dec) coordinates. Easily scriptable.
Given those, from I download a subset of the GAIA catalogue centred on the target and wide enough to include all the comparisons. Quarter to half the FOV is a reasonable estimate. https://vizier.cds.unistra.fr/viz-bin/VizieR-3?-source=I/350&-out.max=50&-out.form=HTML%20Table&-out.add=_r&-out.add=_RAJ,_DEJ&-sort=_r&-oc.form=sexa is a starting point. Customize the search fields until you have nailed down the query you want, then copy the URL for use as a prototype in subsequent searches. I tend to ask for the J2000 coordinates, either G magnitude or RP magnitude (depending on whether the images were unfiltered or V for the former, R or SR for the latter) and its error, and the G-RP value. Ask for lots of lines in tsv format.
Given that data, filter out all stars which are more than a few magnitudes brighter or fainter than the target. Reject all stars which are markedly different colour from your target. Finally, search in the remainder for stars which lie within a few arcsec of the list of coordinates you produced earlier. Remember that stars have proper motions; I have been bitten by this one before!
After all that, you have a sequence of comparison stars ready to be fed into your regular photometry program.
This is my procedure for exoplanets where good sequences do not exist at, say, AAVSO, and for asteroids where they rarely do so.
If you speak Perl, there’s a good chance that much of the scripting required can be provided. Contact me off-list if you wish to give it a try.
Good luck!
Grrr. Why can’t we edit posts for at least a short time after posting?
I forgot to add: ImageMagick comes with Windows distributions, so (AFAIK, I don’t do Windows) you get dcraw for free.
Another thought: check this link – https://imagemagick.org/script/download.php
Completely free and, on my systems at least, thoroughly capable of conversion between almost any image format and almost any other, not to mention a vast amount of image munging abilities.
Thanks Callum.
An impressive process. 1.8 pounds of silver for each treatment! I hope they recovered the excess.
They have been named Nebucula M{aj,in}or for a very long time now.
Remember, Saturn ate his children and Jupiter has some rather controversial sexual activities in his past.
I think we decided the limiting mag was 3ish elsewhere on the sky.
I came to a similar conclusion (though perhaps half a mag fainter) when attempting to observe Venus occulting sigma Sgr some years back. The actual occultation was clouded out but 20 minutes after the star was very easily seen in a 27.5cm Maksutov Cassegrain.
It was after that episode that I became disillusioned by Asimov’s Nightfall. A superb story but the idea that their astronomers living in a globular cluster couldn’t see stars in the daytime beggars belief. Venus at its brightest is a relatively easy daylight naked eye object here on Earth and some claim to be able to see Sirius.
With a modern CMOS sensor I imagine I could do a lot better now.
Or a modern CCD for that matter. A SX 814 works beautifully down to 2ms and was used for my Pleiades imaging.
Yes, a very nice video. Stacking the frames and using something like FABADA to remove the noise and you should end up with a high SNR and, from that, estimate a plausible limiting magnitude.
FWIW, total cloud cover here right now in La Palma but at least it isn’t raining.
OK, you guys, when are you going to start imaging Messier objects? M35, M36 and M37 are well placed right now. 😉
Nick: sure.
It is easy, in my experience, to see 2nd magnitude stars through a telescope in daylight. Some decades ago Venus occulted Nunki, or sigma Sgr. From central Oxford the critical moments were clouded out but 20 minutes or so later the star was very easily visible in a 27.5cm Mak-Cas. I guess the limiting visual magnitude on that occasion was around 4 to 4.5.
What’s a summer blue daytime sky?
Anyway, interesting calculation. The wonderful book “Sunsets, twilights and evening skies” by Aden and Marjorie Meinel contains the attached plot. It indicates a factor of 70 million between a perfect night sky and the noon zenith sky. That is 2.5 * log10(70E6) = 19.6 mags. Assuming a perfect night sky to be 22 mags per square arcsec that would put the noon daytime sky at about 2.4 mags per square arcsec so a bit brighter than you calculated.
The surface brightness of the Full Moon is around 3.4 mags per arcsec so that would imply that it is about 40% the surface brightness of the daytime sky which would be easily detectable with the naked eye. That is something you should be able to demonstrate easily by taking an image and measuring it.
The cloudless sky is, of course, not white. Neither is it unpolarized. The use of a polarizing filter can make a big difference in its brightness but a more important method of darkening the sky is to observe through a red or near infrared filter.
I have already posted images of 6th and 7th magnitude Pleiads taken not too long after local noon. With my kit I estimate that I should be able to reach 12th magnitude with a Sloan i’ filter. It will be necessary to take numerous subs where the stars are almost but not quite saturated and then remove the almost as bright sky background in software.
Well, if we take Ireland as being 500 km long and the nearest Mars comes to the Earth as 60 million km then the flag would subtend around 500/60E6 = 8 microradians or about 2 arcsec so a Martian Damian Peach would definitely be able to resolve it.
Or our Martin Lewis, for that matter, who quite often produces of images showing surface details on the Galilean satellites of Jupiter, all of which are less than 2 arcsec across.
It is the dark side of the moon in the same way that Africa is the dark continent.
And, indeed, it is all dark. The albedo is comparable with fresh asphalt.
The sky over the northern hemisphere was much clearer than usual in mid-September 2001 There is little doubt that contrails have a significant effect on the amount of cloud cover.
What a nice little high-voltage supply you have built for your GM tube!
What voltage is required? I ask because I had to replace my fly-zapper recently. The blue-through-UV LEDs had died but the 4kV power supply still works fine. Perhaps it could be re-purposed.
I am also tempted to build a spark chamber. Lots of fine wires across a cube about 1m in each dimension with each wire being just higher than the breakdown voltage of undisturbed air. Such a beast shows muon tracks very nicely. Elfin safety dictates that the whole be encased in something like Perspex sheets to keep sensitive bodily parts away from the zappy things.
Hah! The FITS files were too big. Here they are at 50% scale and PNG format.
Attachments:
I have now done a little more analysis of the images taken on 2024-02-16 and believe that I have identified three stars in M45.
The first step was to co-add all the images which did not show any stars and use the result as a flat field. Not having taken any true flats with the i’ filter this was the best I could do. It actually worked extremely well when applied to the images which did contain stars.
It was quite impossible to put a WCS on the images so I examined each for distinctive objects which may be found by comparing with the DSS2 survey. I knew the image scale (0.6 arcsec/pix) and approximate camera angle (-177 degrees) so when a double star was found on image number 47, I could tell that the centroids were calculated as 9.5arcsec apart and at a PA of 225 degrees, the primary being markedly brighter than the secondary. Wandering around the Pleiades I came across HD23964A and HD23964C in SIMBAD and cross-referenced with the Washington Double Star catalog where their separation is given as 10.4arcsec in PA 235 degrees with magnitudes of I=6.74 for component A and (R=9.71, J=8.93) for component C. Very satisfactory!
From that the approximate error in the RA and Dec positioning of the mount could be calculated; it came to about 1 minute in RA and -0.3 degrees in declination.
Another bright star, slightly brighter than HD23964, was found in image number 40. Sure enough 26 Tau, at magnitude V=6.46 and J=5.68, was found well within an arcminute of the predicted position. I am reasonably confident of this identification.
Given how easy it is to pick up 9th magnitude objects in the near infra-red with an exposure where the sky almost but not quite saturates the CCD, I think I’ll try to find some more Messier objects in daylight. Call me crazy if you wish.
The attached images show these two objects.
https://www.mdpi.com/2218-1997/9/9/387 is a fascinating paper. A number of periodicities in muon flux are detectable. A strong signal with a periodicity of 125 days is found, along with a diurnal variation and one which correlates well with the temperature of the Earth’s atmosphere. The global magnetic field of the Sun influences the muon intensity and shows up as a 27 day variation.
However, another variation of about 64 days appeared at two solar maxima (but not all of them). I find this surprising!
